Aqueous phosphoric acid (85 wt %) is an effective, environmentally benign reagent for the deprotection of tert-butyl carbamates, tert-butyl esters, and tert-butyl ethers. The reaction conditions are mild and offer good selectivity in the presence of other acid-sensitive groups, including CBZ carbamates, azetidine, benzyl and methyl esters, TBDMS, and methyl phenyl ethers. The mildness of the reaction is further demonstrated in the synthesis of clarithromycin derivative, in which a tert-butyl ester is removed in the presence of cyclic carbamate, lactone, ketal, acetate ester, and epimerizable methyl ketone functionalities. The reaction preserves the stereochemical integrity of the substrates. The reactions are high yielding, and the workup is convenient.

Respiratory tract bacterial strains are becoming increasingly resistant to currently marketed macrolide antibiotics. The current alternative telithromycin (1) from the newer ketolide class of macrolides addresses resistance but is hampered by serious safety concerns, hepatotoxicity in particular. We have discovered a novel series of azetidinyl ketolides that focus on mitigation of hepatotoxicity by minimizing hepatic turnover and time-dependent inactivation of CYP3A isoforms in the liver without compromising the potency and efficacy of 1.

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1,3-Dimethyl 2-imidazolidinone (DMI) is of lower toxicological risk than 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU), hexamethyl-phosphorus triamide (HMPT), and hexamethylphosphoramide (HMPA). Formation of dialkylation byproducts is a common problem in lactone alkylation. DMI, used in stoichiometric amount, increases the rate of alkylation of γ-butyrolactone 1 by >30-fold, therefore minimizing the dialkylation in multi-kilogram preparations. The isolated yield of the monoalkylated product 2 is >90%. The reaction protocol is also demonstrated to work on other lactone substrates and alkylating agents.